This invention relates generally to hydraulically actuated automotive disc brake assemblies and more particularly to brake shoe actuator construction for reducing brake pad drag on the rotor in such assemblies.
Brake pad drag is a phenomenon which results in automotive disc brake assemblies when the brake pads remain in contact with the rotor surface after the piston has been retracted. Brake pad drag is undesirable because it reduces usable vehicle horsepower and adversely impacts fuel economy. Additionally, brake pad drag may produce undesirable noise which can interfere with the quiet ride of the motor vehicle.
Several efforts to reduce brake pad drag have been made in the past. For example, many current disc brake assemblies use roll-back seals in combination with two- or three-pronged retainer clips riveted to the backing plate of the inner brake shoe assembly to retract the brake pad from the rotor. The roll-back seal, placed between the piston and the cylinder, is designed to retract the piston into the cylinder from 0.005 to 0.015 inches. Ideally, the pronged retainer clip engages the piston so that when the roll-back seal retracts the piston, the inner brake pad retracts from the rotor equidistant with the piston. In practice, however, the retainer clip is prone to bending, misalignment during assembly or loss of spring tension which prevents the clip from functioning as designed. As a result, substantial lost motion between the inner brake pad and the piston is not prevented which may result in dragging of the brake pad against the rotor.
A need therefore exists for an inner brake shoe assembly which positively retains the brake shoe with the piston to eliminate brake pad drag when the piston retracts.